ESV Ultra--White Substrate provides the whitest calcium carbonate based substrate available to the marine aquarium hobbyist. This translates to a greater efficiency of lighting systems by provinding increased levels of reflected light from the aquarium bottom. Available in a fine grade with a particle size of 0.43 - 1.18 mm (.016 - .047 in. ) and a coarse grade with a particle size of 1.40 - 3.35 mm (.056 - .132 in.). Available in 50lbs bags.